Various types of fluid recovery systems have been devised for collecting fluid from a formation at the surface of a well. In the petroleum recovery industry, a common fluid recovery system is a beam pump which reciprocates a rod passing through a tubing string to a downhole pump. Although beam pumps have been widely used in fluid recovery systems, they have inherent limitations which are becoming of increasing concern. Beam pumps by their very nature require a large amount of space and are typically quite noisy. Beam pumps also do not work well in highly deviated holes due to the wear inherent with the reciprocating rods. The rod string between the beam pump and the downhole pump is also expensive and contributes to tubing failures. A further disadvantage of rod-type pumps is that fluid under high pressure may bypass the closing valve and thus flow back toward the formation during the initial portion of the down stroke of the rod.
Another type of fluid recovery system for collecting formation fluid from a well utilizes an electric submersible pump. These pumps produce large volumes of fluids, but they have difficulty handling fluids with high solids content and/or fluids with a high percentage of gas. Electric submersible pumps are also expensive to install and maintain.
Some fluid recovery systems have utilized positive displacement or screw-pumps which utilize a rotating rod string. These pumps practically are limited to relatively shallow depths. The rotating rod string does not perform well in highly deviated wells, and also contributes to tubing wear.
One other type of fluid recovery system is referred to as a gas lift system. This system generally depends upon the injection of gas in the production string, and is expensive to operate, particularly when gas must be transported, compressed, and pumped into a well.
Jet pumps are currently used on a small percentage of wells to recover formation fluids. Jet pumps have significant advantages, but conventionally have required relatively expensive and high maintenance surface pumps to generate the power fluid for operating the downhole jet pump. An improved jet pump is disclosed in U.S. Pat. No. 5,372,190.
Some well operators have incurred the expense of a horizontal ESP (electric pumps) at the surface of a well to power a downhole pump. Horizontal ESP's are expensive, and also require a large amount of energy.
Diaphragm pumps have been used for various applications, including particularly those involving the pumping of chemicals, food products, and sewage. Diaphragm pumps are disclosed in U.S. Pat. Nos. 3,775,030, 3,884,598, 4,086,036, 4,433,966, 4,523,902, 5,188,515, 5,192,198, 5,306,522, 5,707,219, and 6,065,389. A diaphragm pump with two or more diaphragms is disclosed in U.S. Pat. No. 6,174,144. Diaphragm pumps have also been proposed as a downhole pump in a well, as evidenced by U.S. Pat. Nos. 6,017,198 and 6,595,280.
An improved fluid recovery system for collecting formation fluids at the surface of a well preferably utilizes a high reliability and relatively low cost downhole pump, and an efficient, relatively low cost, low maintenance and high reliability surface pump.
The disadvantages of the prior art are overcome by the present invention, and an improved fluid recovery system for collecting formation fluids at the surface of a well is hereinafter disclosed. The system utilizes an efficient downhole jet pump in combination with a surface diaphragm pump for passing the power fluid to the jet pump.